Constrained cure component attach process for improved IC package warpage control

ABSTRACT

An apparatus, comprising a first platform comprising a first working surface having a first non-planar portion; and a second platform comprising a second working surface having a second non-planar portion, wherein: the second working surface is opposite the first working surface, a distance between the first working surface and the second working surface is adjustable, the first non-planar portion comprises a first curved portion, and the second non-planar portion comprises a second curved portion opposite the first curved portion.

BACKGROUND

Packaging for microelectronic devices is facing increasing demand forsmaller dimensions. This trend is driven by consumer demand forincreasing portability of computing devices such as smart phones andlaptops. Currently, there is an industry-wide trend to reduce IntegratedCircuit (IC) package dimensions to accommodate the trend for ultrathinhigh performance smart phones, where IC package thickness, as well asfootprint, is reduced without impacting device performance. However,increasingly thinner packages are subject to high warpage, drasticallyimpacting yield.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the disclosure will be understood more fully from thedetailed description given below and from the accompanying drawings ofvarious embodiments of the disclosure, which, however, should not betaken to limit the disclosure to the specific embodiments, but are forexplanation and understanding only.

FIG. 1A illustrates a profile view of a constrained IC package assembly(CPA) bonding tool, according to some embodiments of the disclosure.

FIG. 1B illustrates a profile view of a CPA bonding tool, according tosome embodiments of the disclosure.

FIG. 2 illustrates a profile view of a second embodiment of a CPA toolwith a three-point bending jig having a flat spacer, according to someembodiments of the disclosure.

FIG. 3 illustrates a profile view of a third embodiment of CPA tool witha three-point bending jig having a round spacer, according to someembodiments of the disclosure.

FIG. 4A illustrates a cross-sectional view of a CPA tool having an opencavity pedestal, according to some embodiments of the disclosure.

FIG. 4B illustrates a cross-sectional view of a CPA tool having an airpressure workpiece constraint system, according to some embodiments ofthe disclosure.

FIG. 5A illustrates a cross-sectional view of a molding tool for ICpackage over-mold having convex mold chases, according to someembodiments of the disclosure.

FIG. 5B illustrates a cross-sectional view of a molding tool havingconcave mold chases, according to some embodiments of the disclosure.

FIG. 6A illustrates a profile view of a CPA tool having concavethermocompression bonding (TCB) heads with a constrained die backsidestiffener attach workpiece during a IC package assembly process,according to some embodiments of this disclosure.

FIG. 6B illustrates an exemplary plot for correlating the magnitude ofconcave warpage introduced into a IC package during cure and the warpageof the IC package at 25° C., according to some embodiments of thedisclosure.

FIG. 7 illustrates a method for an exemplary CPA process embodied in aprocess flow chart, according to embodiments of the disclosure.

FIG. 8 illustrates a constrained cure assembled IC package connectingmultiple dies as part of a system-on-chip (SoC) IC package in animplementation of computing device, according to some embodiments of thedisclosure.

DETAILED DESCRIPTION

In the following description, numerous details are discussed to providea more thorough explanation of embodiments of the present disclosure. Itwill be apparent, however, to one skilled in the art, that embodimentsof the present disclosure may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form, rather than in detail, in order to avoidobscuring embodiments of the present disclosure.

Here, the term “die” generally refers to a chip, or portion ofsemiconductor or insulator substrate supporting at least one integratedcircuit (IC). The die is cut, or diced, usually as multiple copies, froma processed substrate wafer. The die must be packaged for access to thecircuitry integrated on the die.

Here, the term “IC package” generally refers to a self-contained carrierof one or more dies, where the dies are attached to the IC packagesubstrate, and encapsulated for protection, with integrated orwire-boned interconnects between the die(s) and leads, pins or bumpslocated on the external portions of the IC package substrate. The ICpackage may contain a single die, or multiple dies, providing a specificfunction. The IC package is usually mounted on a printed circuit boardfor interconnection with other packaged ICs and discrete components,forming a larger circuit.

Here, the term “stiffener” generally refers to a stiff metal plate orframe attached to a IC package substrate to mitigate bending and warpageof the IC package substrate that may occur during manufacture.

Here, the term “warpage” generally refers to a strain-inducednon-planarity or curvature of an IC package that may occur during orafter assembly. The IC package bows into a concave or convex profile,where “convex” is generally defined as bowing of the IC packagesubstrate upward, or toward an attached die and/or stiffener, and where“concave” is generally defined as bowing of the IC package downward, oraway from an attached die and/or stiffener.

Here, the term “thermal compression bonding” generally refers to amanufacturing method for IC package assembly by tooling that appliesheat and pressure to bond together IC package components such as dies,lead frames and stiffeners. Heat may be applied for solder reflow and/oradhesive curing. The tooling may simultaneously apply force to press thecomponents together as a stack, typically dies, heat spreaders,interposers, stiffeners and/or lead frames on a IC package substrate.The pressure may be applied during the heating cycle to increase contactbetween bonding surfaces, ensuring reliability of the finished ICpackage.

As an IC package thickness is reduced, the IC package is subject towarpage due to temperature-induced strain on IC package components. Muchof the strain results from a coefficient of thermal expansion (CTE)mismatch between materials of the IC package components when subject tothermal cycling. An example of thermal cycling during IC packageassembly is solder reflow, where packages are subjected to temperatureexcursions up to 260° C. for several minutes. Other thermal cyclinginvolves adhesive curing, where epoxy adhesives may be used forattachment of IC package components such as integrated heat spreadersand lead frames to the IC package substrate.

In current IC package assembly processes, the adhesive bonding ofcertain components is typically performed in a thermocompression bonding(TCB) tool, where the TCB tool keeps the substrate and stiffenersubstantially flat during thermal cycling. TCB tools generally comprisetwo platens, with temperature control applied to one or both platens.The workpiece, which here is the partially assembled IC package, iscompressed and held flat between the platens during a heating cycle,where a controlled force is applied to one or both platens. Thetemperature cycle is generally optimized for curing adhesives used inbonding components to a IC package substrate, or to other components.Conventional TCB tool platens are typically thick steel plates, and haveflat work surfaces for even application of heat and pressure to theworkpiece. Force is applied to press and hold IC package componentstogether to assure good bonding while holding the IC package andattached components substantially flat.

After cooling of the IC package, measurable room temperature warpage maybe observed due to CTE mismatch of bonded IC package components.Compressive and tensile strain may be present within the packagessubstrate, causing the convex bowing (e.g., compressive strain) orconcave bowing (e.g., tensile strain).

To counteract warpage, a stiffener may be included in the IC packageassembly by attachment to the substrate. The role of the stiffener is toconstrain the IC package to be reasonably flat by counteringthermally-induced strain in the IC package substrate. Stiffeners, whichare typically high modulus metal plates or frames, are oftenadhesive-bonded at high temperatures (e.g., approximately 160° C.) in aTCB tool to a IC package substrate before or after die attachment, toreduce warpage and balance the distribution of CTE in the IC package.The IC package and stiffener are held flat during the thermocompressionbonding.

The CTE and modulus of the stiffener may be optimized for compatibilitywith a particular IC package. Dimensions are chosen to be compatiblewith the IC package x-y footprint. As the latter (IC package x-ydimensions) become smaller to meet consumer demand for more compactmobile devices, there is less IC package substrate surface to which astiffener may be bonded. Therefore, for the stiffener to be effective incontrolling IC package warpage, the stiffener may be made thicker tocompensate for the smaller bonding area. The requirement for thickerstiffeners to compensate for smaller IC package footprint isantithetical to the effort to produce thinner packages.

Often, a stiffener is optimized to reduce warpage at room temperature,for instance, after adhesion of IC package an integrated heat spreader.Warpage may be apparent again, for instance, when the IC package isthermally cycled to higher temperatures for further processing. Anotherexample is when a finished IC package is soldered to a printed circuitboard in a SMT reflow oven, where reflow temperatures can peak at 260°C. Warpage may be critical during this stage, as bowing of the ICpackage substrate can be several hundred microns to a millimeterout-of-plane.

Described herein is a IC package assembly tool and method and forcontrolling and optimizing IC package warpage that does not require theneed for thick stiffeners, in accordance with some embodiments.Embodiments of the IC package assembly tool, herein referred to as aconstrained IC package attach (CPA) tool, and a method for attachingcomponents to a workpiece comprising a IC package substrate. The CPAtool has non-planar working surfaces that are engineered to hold aworkpiece into a constrained out-of-plane shape during thermal cycling,in contrast to conventional thermocompression bonding (TCB) heads thathave substantially flat working surfaces for holding a workpiece in anominally flat shape. The direction of bowing may be convex or concave.The workpiece is constrained into an out-of-plane bowed shape in the CPAtool and is held in the constrained shape during temperature cycling tointroduce a predetermined, or engineered warpage into the IC package.The predetermined warpage that is introduced to the IC package substrateand attached components counteracts the natural warpage that aconventionally assembled IC package may exhibit at certain temperatures.The direction of the predetermined warpage may be convex to negate anatural concave warpage. The magnitude of the introduced warpage may bepredetermined by empirical methods to result in a zero warpage, orsubstantially flat geometry, at a specific temperature range.

As an example, during a stiffener attach operation, the stiffener andsubstrate are constrained to bow into a specific warpage in a CPA tool.The warpage is predetermined to negate natural warpage that the ICpackage exhibits would otherwise exhibit at room temperature, or athigher temperatures, if held flat the during stiffener attach operation.The stiffener adhesive is cured and hardened during temperature cycling,causing the IC package to retain the warpage after removal from the CPAtool.

The magnitude and direction of the introduced warpage is in generaltemperature dependent. In some embodiments, the magnitude of theintroduced warpage is optimized to be substantially zero at ambienttemperatures (e.g., room temperature, 25° C.), and non-zero at highertemperatures. In some embodiments, the magnitude of the introducedwarpage is optimized to be substantially zero at solder reflowtemperatures (e.g., 220° C. to 260° C.), and non-zero at lowertemperatures (e.g., 25° C.). In this case, the IC package relaxes fromthe room temperature warpage to a flat geometry (substantially zerowarpage) at solder reflow temperatures. For downstream device assembly,the substantially zero warpage at solder reflow temperatures isadvantageous. For example, the reliability of solder joints is increasedduring attachment of a ball grid array (BGA) IC package to a circuitboard when the IC package relaxes from a warped geometry at roomtemperatures to a flat geometry during the solder reflow process.

In some embodiments, the introduced warpage is optimized to negatenatural warpage that occurs any temperature between room temperatures(approximately 25° C.) to solder reflow temperatures (220° C.-260° C.).The introduced warpage may be determined empirically or by numericalcalculation. By empirical methods, introduced warpage may be optimizedand tuned by systematically varying the magnitude of the constrainedout-of-plane bowing in the CPA tool during an attach process, such as astiffener attach process. The resulting warpage exhibited by the ICpackage at a specific temperature or range of temperatures is correlatedto the magnitude of introduced warpage.

Some embodiments of the CPA tool comprise a TCB head having a curvedbonding surface for introducing a predetermined warpage in the ICpackage during thermocompression bonding of components to the substrate,by pressing the workpiece with a non-planar bond head having curved orotherwise non-planar working surfaces, introducing a predeterminedcurvature to the IC package substrate and its attached components. Thisis in contrast to the conventional method of pressing the workpiece flatduring thermocompression bonding.

According to some embodiments described herein, a predetermined warpageis introduced into a IC package at an elevated temperature duringthermocompression bonding. According to some embodiments describedherein, the out-of-plane curvature of the introduced warpage iscalculated to counteract natural warpage that normally occurs aftertemperature cycling and return to room temperature.

The predetermined warpage is introduced into the IC package substrate,stiffener and other components bonded to the IC package substrate, andconstraining the IC package assembly (e.g., substrate plus pre-bondedcomponents and adhesive) in CPA tool. The CPA tool is equipped withbonding heads that have curved or otherwise non-planar work surfaces. Insome embodiments, the bonding heads are TCB heads.

According to some embodiments, the introduced warpage and naturalwarpage are correlated, however, the magnitude of introduced opposingwarpage may not equate to the magnitude of natural warpage. Themagnitude of introduced warpage that effectively negates natural warpagemay be determined experimentally or by computational methods. Knowledgeof the magnitude of introduced warpage to counteract natural warpage maybe manifested in the curvature or nonplanarity of the CPA tool bondinghead work surfaces.

By way of example, a IC package is known to develop a convex warpagehaving a magnitude (e.g., maximum out-of-plane deflection) of 500microns at room temperature after stiffener bonding. Accordingly, theroom temperature warpage is substantially negated by introducing aconcave warpage into the IC package assembly. As the concave warpage isintroduced at an elevated temperature during thermocompression bondingin the CPA tool, during cooling the CTE mismatch strain will naturallytry to warp the IC package in an opposing curvature. The concave warpageduring curing of the adhesive bonding the stiffener of the IC packagesubstrate counteracts the tendency of the IC package to warp in theopposite direction. The net result is that the net room temperaturecurvature of the IC package assembly is approximately zero.

According to some embodiments, CPA tool bonding head work surfaces havea built-in curvature or non-planarity having a prescribed geometry tointroduce a warpage calculated to negate natural warpage of theworkpiece after thermal cycling during a particular operation. In someembodiments, CPA tool bond heads comprise a three-point or three-linecontact jig, where the workpiece is suspended form parallel edges, thenpressed downward from above the workpiece by a protrusion contacting theworkpiece at or near the middle.

Throughout the specification, and in the claims, the term “connected”means a direct connection, such as electrical, mechanical, or magneticconnection between the things that are connected, without anyintermediary devices.

The term “coupled” means a direct or indirect connection, such as adirect electrical, mechanical, or magnetic connection between the thingsthat are connected or an indirect connection, through one or morepassive or active intermediary devices.

The term “circuit” or “module” may refer to one or more passive and/oractive components that are arranged to cooperate with one another toprovide a desired function. The term “signal” may refer to at least onecurrent signal, voltage signal, magnetic signal, or data/clock signal.The meaning of “a,” “an,” and “the” include plural references. Themeaning of “in” includes “in” and “on.”

The vertical orientation is in the z-direction and it is understood thatrecitations of “top”, “bottom”, “above” and “below” refer to relativepositions in the z-dimension with the usual meaning. However, it isunderstood that embodiments are not necessarily limited to theorientations or configurations illustrated in the figure.

The terms “substantially,” “close,” “approximately,” “near,” and“about,” generally refer to being within +/−10% of a target value(unless specifically specified). Unless otherwise specified the use ofthe ordinal adjectives “first,” “second,” and “third,” etc., to describea common object, merely indicate that different instances of likeobjects are being referred to, and are not intended to imply that theobjects so described must be in a given sequence, either temporally,spatially, in ranking or in any other manner.

For the purposes of the present disclosure, phrases “A and/or B” and “Aor B” mean (A), (B), or (A and B). For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B),(A and C), (B and C), or (A, B and C).

Views labeled “cross-sectional”, “profile” and “plan” correspond toorthogonal planes within a cartesian coordinate system. Thus,cross-sectional and profile views are taken in the x-z plane, and planviews are taken in the x-y plane. Typically, profile views in the x-zplane are cross-sectional views. Drawings are labeled with axes toindicate the orientation of the figure.

FIG. 1A illustrates a profile view of CPA bonding tool 100 a, accordingto some embodiments of the disclosure.

In FIG. 1A, CPA bonding tool 100 a comprises upper thermocompressionbonding (TCB) head 101 and lower TCB head 102, shown disposed above andbelow curved workpiece 103. In the illustrated embodiment, upper TCBhead 101 comprises concave curved work surface 104. Work surface 105 oflower TCB head 102 is also convex, and has a curvature that issubstantially the same as that of work surface 104. Upper TCB head 101and lower TCB head 102 comprise one or more of: steel, aluminum, copper,or brass, and/or alloys thereof.

In some embodiments, the particular shape of concave and convex worksurfaces 104 and 105 has a curvature to constrain workpiece 103 into abowed shape having a predetermined magnitude. In some embodiments, thepredetermined magnitude of bowing or warpage may be used for aparticular IC package type and measured warpage that occurs after aparticular thermal cycle.

In some embodiments, workpiece 103 comprises a IC package assemblystack. In the illustrate embodiment of FIG. 1A, workpiece 103 comprisesIC package substrate 106 and stiffener 107. In the exemplary embodimentshown in FIG. 1A, CPA bonding tool 100 a is implemented as a constrainedstiffener attach (CSA) tool, where the curvature workpiece 103 isconstrained during the CSA process.

In some embodiments, stiffener 107 and IC package substrate 106 arecompliant under stress, and follow the curvature of work surfaces 104and 105 when pressed between upper TCB head 101 and lower TCB head 102.In some embodiments, the bonding adhesive (not shown) is cured duringthe temperature cycle, introducing a permanent bowing or warpage intoworkpiece 103.

As is shown below, CPA bonding tool 100 may be configured for attachmentof other IC package components, such as integrated heat spreaders (IHS),interposers, and dies.

FIG. 1B illustrates a profile view of CPA bonding tool 100 b, accordingto some embodiments of the disclosure.

In FIG. 1B, CPA bonding tool 100 b comprises upper TCB head 101′ andlower TCB head 102′. TCB head 101′ comprises convex work surface 104′.TCB head 102′ comprises concave work surface 105′. In the illustratedembodiment, work surfaces 104′ and 105′ have curvature opposite that ofcounterpart work surfaces 104 and 105 in FIG. 1A. The curvature ofworkpiece 103′ follows the curvature of the upper work surface 104′ andlower work surface 105′, bowing IC package substrate 106 and stiffener107 into a concave warpage, as shown in FIG. 1B. The concave introducedwarpage of workpiece 103′ is opposite that of workpiece 103 in FIG. 1A.

The introduction of concavity or convexity to workpiece 103 (FIG. 1A)and of 103′ depends on the natural warpage that is experienced by a ICpackage assembled by flat component attach methods. In some embodiments,workpiece 103′ is bowed into a concave warpage during constrainedstiffener attach (CSA). The concave introduced warpage may negate atendency of a IC package to undergo a convex natural warpage at 260° C.,experienced by a conventionally assembled IC package. Thus, the chosenconstraint curvature is dependent on the direction of natural warpage tobe negated by the introduced warpage, and may be optimized and tuned tonegate natural warpage at any temperature. In addition, factors such asnumber of dies attached to the substrate, or that will be attached,final IC package thickness, may determine the amount and direction ofcurvature to introduce into the IC package assembly.

FIG. 2 illustrates a profile view of a second embodiment of CPA tool 200with a three-point bending jig having a flat spacer, according to someembodiments of the disclosure.

In FIG. 2, constrained IC package assembly (CPA) tool 200 comprises TCBhead 201 having a flat profile, and pedestal stand 202 having three flatpedestals 203, 204 and 205. Sandwiched between pedestals 203-205 and TCBhead 201 is workpiece 206, which is shown in FIG. 2 pinned between flatspacer 207 and pedestals 203-205. Pedestals 203-205 are spaced atdistances commensurate with length of workpiece 206. In someembodiments, pedestals 203 and 205 are disposed under parallel edges ofworkpiece 206. In some embodiments, pedestals 203 and 205 are planar andhave a larger z-height than center pedestal 204. The recess of centerpedestal permits workpiece 206 to bow when TCB head 201 is lowered,pressing flat shim 207 against workpiece 206. In some embodiments,workpiece 206 is thus constrained in the bowed shape shown during acomponent attach process, and may have an introduced concave warpagecorresponding to the thickness of flat spacer 207 after temperaturecycling in CPA tool 200. In some embodiments, TCB heads 201 and 202 areinverted, constraining workpiece 206 into a convex bow.

In some embodiments, heat is transferred to workpiece 206 at least inpart through convective modes from TCB head 201. In some embodiments,heat transfer to workpiece 206 is made at least in part by conductionthrough pedestals 203-205. In some embodiments, heat transfer toworkpiece 206 is at least in part made by conductive mode through flatspacer 207. While TCB head 201 and pedestal stand 202 of CPA tool 200have smaller working surface area for conductive heat transfer toworkpiece 203, the distance between workpiece 203 and non-contactingheated surfaces of TCB head 201 and pedestal stand 202 is exaggerated inFIG. 2. In some embodiments, actual gap distances between workpiece 203and non-contacting surfaces is up to 500 microns. Thus, effectiveconvective heat transfer may be made from non-contacting surfaces toworkpiece 203.

In some embodiments, flat spacer 207 is removable for interchanging withshims of different thicknesses. The magnitude of the introduced warpagemay be controlled by the thickness of flat spacer 207. In someembodiments, central pedestal 204 is adjustable to accommodateadjustable magnitudes of warpage determined at least in part by flatspacer 207. In some embodiments,

FIG. 3 illustrates a profile view of a third embodiment of CPA tool 300with three-point bending jig having a round spacer, according to someembodiments of the disclosure.

In FIG. 3, CPA tool 300 comprises upper TCB head 301 and lower TCB head302 attached round spacers 303, 304 and 305. Workpiece 306 is suspendedover lower PCB head by round spacers 303 and 305, disposed underneathopposite parallel edges of workpiece 306. In some embodiments, workpiece306 is constrained into a concave bowed shape by spacer 304 disposednear or at the middle of workpiece 306 and pressing downward. Roundspacers 303-305 provide point or line contacts to workpiece 306,allowing accurate positioning. In some embodiments, round spacers303-305 have diameters ranging up to 500 microns. In some embodiments,round spacers 303-305 are welded to TCB heads 301 and 302. In otherembodiments, round spacers 303-305 are machined into the workingsurfaces of TCB heads 301 and 302. Round spacers 303-305 may comprisematerials including, but not limited to, steel, stainless steel, copper,brass, and aluminum.

In some embodiments, heat transfer to workpiece 306 may be made byconvective modes from heated upper TCB head 301, lower TCB head 302 orfrom both TCB heads 301 and 302. In some embodiments, distances fromsurfaces of the TCB heads to workpiece 306 are 500 microns or less,allowing efficient heat transfer by convective and radiative modes. Insome embodiments, CPA tool 300 is placed in a heated chamber, such as anoven, to ensure uniform distribution of heat to workpiece 306.

Warpage introduced into workpiece 306 may be controlled by the diametersof round spacers 303-305. In some embodiments, TCB heads 301 and 302 areinterchangeable within CPA tool 300, allowing diameters of round pacers303-305 to be changed.

FIG. 4A illustrates a cross-sectional view of CPA tool 400 a having anopen cavity pedestal, according to some embodiments of the disclosure.

In FIG. 4A, CPA tool 400 a comprises pedestal 401 having an open cavity402, over which workpiece 403 is suspended without constraints. In someembodiments, workpiece 403 is suspended along opposing edges on ledges404. Workpiece 403 is constrained between stylus 405, disposed over thecenter region of workpiece 403, and ledges 404 disposed at or nearopposing edges of workpiece 403. In some embodiments, ledges 404 andstylus 405 provide a three-point contact clamp system to constrainworkpiece 403 into a bowed shape, introducing a warpage to workpiece403. In some embodiments, stylus 405 is attached to plunger 406, whichis coupled to a drive mechanism (not shown) for raising and loweringstylus 405 away from and towards workpiece 403, as indicated by the dualarrowheads in FIG. 4A. In the illustrated embodiment, plunger 403 isabutted against workpiece 403, constraining workpiece 403 in a concavebow.

In some embodiments, workpiece 403 comprises IC package substrate 407and stiffener 408. Warpage may be introduced during thermal cycling of astiffener attach process, where the magnitude of warpage is set bydistance IC package substrate 407 and stiffener 408 are bowedout-of-plane. In some embodiments, the magnitude of warpage is adjustedby the vertical positioning of stylus 405. Stylus 405 may abut againstworkpiece 403 with a predetermined amount of force to cause workpiece403 to bow with a predetermined magnitude. In some embodiments, pedestal401 is heated. In some embodiments, cavity 402 is less than 1 mm deep,allowing efficient heat transfer to workpiece by convective andradiative modes.

FIG. 4B illustrates a cross-sectional view of CPA tool 400 b having anair pressure workpiece constraint system, according to some embodimentsof the disclosure.

In FIG. 4B, CPA tool 400 b comprises pedestal 401′ having vacuum ports409 opening into cavity 402′. Pedestal 401 comprises ledges 404,disposed at opposing edges of workpiece 403. In some embodiments,workpiece 403 is suspended over cavity 402′. In some embodiments, cavity402′ is a vacuum chamber. In some embodiments, cavity 402′ is undervacuum, causing the atmospheric pressure below workpiece 403 to be lowerthan the atmospheric pressure above workpiece 403, bowing workpiece 403to introduce a concave warpage into workpiece. 403. In the illustrateembodiment, workpiece 403 comprises IC package substrate 407 andstiffener 408. In other embodiments, workpiece 403 comprises othercomponents, including, but not limited to, one or more dies, anintegrated heat spreader, a lead frame, and an interposer.

Cavity 410 is disposed above workpiece 403, opposite cavity 402′. Insome embodiments, cavity 410 is a portion of upper TCB head 411, andopen at the intersection of the cavity 410 with working surface denotedby the dashed line. In some embodiments, upper TCB head 411 forms a sealwhen in contact with pedestal 401′, and cavity 410 is separated fromcavity 402′ by workpiece 403, as shown in FIG. 4B. In some embodiments,cavity 410 is pressurized by introduction of pressurized gas, forming apressure chamber. Pressurized gases include, but are not limited to,air, nitrogen, helium, and argon. Force applied to the top of workpiece403 by pressurized gas confined within chamber 410 bows workpiece 403into a concave shape. In some embodiments, vacuum applied to cavity 402′assists bowing of workpiece 403. Downward-pointing arrows in FIG. 4Bindicate direction of applied force, both from positive pressure of thepressurized gas above workpiece 403 and from negative pressure of thevacuum applied below workpiece 403.

In some embodiments, workpiece 403 may be bowed into a convex shape byreversal of chamber pressurization. In some embodiments, cavity 410 is avacuum chamber, and cavity 401′ is pressurized. In some embodiments,workpiece 403 is clamped at opposing edges to enable IC packagecomponents to face upwards while constrained to bow when pressure isapplied from below.

In some embodiments, upper TCB head 411 and pedestal 402′ are heated.Heat may be transferred to workpiece 403 by convective and radiativemodes. In some embodiments, chamber 410 and cavity 402′ have depths notexceeding 1 mm for efficient heat transfer from chamber surfaces toworkpiece 403. In some embodiments, CPA tool 400 is placed in a heatedchamber, such as an oven.

FIG. 5A illustrates a cross-sectional view of molding tool 500 a for ICpackage over-mold having convex mold chases, according to someembodiments of the disclosure.

In FIG. 5A, CPA tool 500 a comprises injection molding head 501, whichcomprises upper convex mold chase 502 and lower convex mold chase 503.Upper convex mold chase 502 and lower convex mold chase 503 enclose moldchamber 504, within which workpiece 505 is enclosed. Workpiece 505comprises IC package substrate 506, stiffener 507 and die 508. Sprue 509is disposed above mold chamber 504, and opens into mold chamber 504.Piston 510 inserts into sprue 509. During the molding of workpiece 505,molten mold compound 511 is injected under pressure into mold chamber504 through sprue 509. Piston 510 presses on molten mold compound 511,forcing it through sprue 509 into mold chamber 504.

In some embodiments, workpiece 505 is constrained within mold chamber504 to bow into the illustrated shape, introducing a convex warpage intoworkpiece 505. Upper convex mold chase 502 molds a substantiallyidentical convex curvature into mold compound 511. The curvature ofupper and lower convex mold chases 502 and 503, respectively, may bespecific to counteract a known natural warpage of a particular ICpackage. In some embodiments, the same CPA tool 500 a may be used formore than one IC package by inclusion of interchangeable upper and lowerconvex mold chases 502 and 503. In some embodiments, upper and lowerconvex mold chases 502 and 503 are removable and interchangeable withcorresponding parts having different curvatures.

FIG. 5B illustrates a cross-sectional view of molding tool 500 b havingconcave mold chases, according to some embodiments of the disclosure.

In FIG. 5B, CPA tool 500 b comprises injection molding head 501′, whichcomprises upper concave mold chase 502′ and lower concave mold chase503′. Upper concave mold chase 502 and lower concave mold chase 503′enclose mold chamber 504, within which workpiece 505′ is enclosed.Workpiece 505′ comprises IC package substrate 506, stiffener 507 and die508. Sprue 509 is disposed above mold chamber 504, and opens into moldchamber 504. Piston 510 inserts into sprue 509. During the molding ofworkpiece 505, molten mold compound 511 is injected under pressure intomold chamber 504 through sprue 509. Piston 510 presses on molten moldcompound 511, forcing it through sprue 509 into mold chamber 504.

In some embodiments, workpiece 505′ is constrained within mold chamber504 to bow into the illustrated shape, introducing a concave warpageinto workpiece 505′. Upper concave mold chase 502′ molds a substantiallyidentical concave curvature into mold compound 511. The curvature ofupper and lower concave mold chases 502′ and 503′, respectively, may bespecific to counteract a known natural warpage of a particular ICpackage. In some embodiments, the same CPA tool 500 b may be used formore than one IC package by inclusion of interchangeable upper and lowerconcave mold chases 502′ and 503′. In some embodiments, upper and lowerconcave mold chases 502′ and 503′ are removable and interchangeable withcorresponding parts having different curvatures.

FIG. 6A illustrates a profile view of CPA tool 100 a having concave TCBheads with a constrained die backside stiffener attach workpiece duringa IC package assembly process, according to some embodiments of thisdisclosure.

In FIG. 6A, CPA tool 100 a comprises upper thermocompression bonding(TCB) head 101 and lower TCB head 102, shown disposed above and belowworkpiece 601. In the illustrated embodiment, workpiece 601 comprises ICpackage substrate 602, die 603 and die backside stiffener 604. In someembodiments, die 603 is solder bonded to IC package substrate 602 in anearlier solder reflow operation. In a present operation, die backsidestiffener 604 is attached in the present operation. An adhesive (notshown) is applied in an earlier operation. In some embodiments, theadhesive may be in a liquid state or partially cured in the illustratedembodiment.

Workpiece 601 is abutted against work surfaces 104 and 105 byapproaching upper TCB head 101 and lower TCB head 102. All components ofworkpiece 601 are constrained to bow into a concave curvature bycompressive force imposed by upper and lower TCB heads 101 and 102. Insome embodiments, upper TCB head 101 is heated. In some embodiments,lower TCB head 102 is heated. In some embodiments, both upper and lowerTCB heads 101 and 102 are heated. During temperature cycling, the diebackside stiffener adhesive cures and solidifies, creating a permanentconcave warpage of workpiece 601.

The magnitude of the introduced concave warpage of workpiece 601 isdetermined by the curvature of work surfaces 104 and 105 of upper andlower TCB heads 101 and 102, respectively. The curvature of worksurfaces 104 and 105 is predetermined by knowledge of the magnitude anddirection of natural warpage of a particular IC package that isconventionally assembled by flat thermocompression bonding. Tocounteract a natural convex warpage, working surfaces 104 and 105 may bemachined to have a concave curvature, the warpage at room temperaturemay be negated by measurement of the room temperature warpage (magnitudeand direction) and determining a magnitude and direction of introducedwarpage that negates or mitigates the natural warpage.

FIG. 6B illustrates exemplary plot 650 for correlating the magnitude ofconcave warpage introduced into an IC package during cure and thewarpage of the IC package at 25° C., according to some embodiments ofthe disclosure.

In FIG. 6B, plot 650 is determined experimentally for determining themagnitude of introduced warpage into a particular IC package duringconstrained IC package assembly (CPA) in order to substantially mitigateIC package warpage at 25° C. In some embodiments, curve 660 of plot 650is fit to several experimental data points. The negative values on theaxes indicate concave warpage, while the positive values indicate convexwarpage. In the illustrated example, the particular IC package exhibitsa natural convex warpage at room temperature (e.g., approximately 20° C.to 25° C.) after the IC package is assembled and having undergoneseveral temperature cycling operations for component attach, includingsolder reflow for die attach. The magnitude and direction of naturalwarpage may depend on the particular materials, dimensions, moduli andCTE mismatch between attached components.

By way of example, to counteract the natural convex warpage that afinished IC package exhibits at room temperatures (e.g., 20° C. to 25°C.) if assembled in a flat geometry, a number of IC package units may beassembled by the CPA process. A correlation curve may be constructed bysystematically varying the magnitudes of introduced warpage. In someembodiments, partially assembled IC package workpieces are constrainedin a CPA tool with different amounts of out-of-plane bowing. Theresidual IC package warpage at room temperature may then be thenmeasured. The resulting correlation plot, such as plot 650, may be usedto determine the final IC package warpage at approximately 25° C., as afunction of the magnitude of warpage introduced during CPA IC packageassembly. As an example, if zero IC package warpage is desired at roomtemperature, a magnitude of warpage introduced during a constrainedattach process (e.g., constrained stiffener attach) optimizationprocedure in the CPA tool may be identified that correlates to zerowarpage at room temperature. The introduced warpage may be optimized forzero IC package warpage at any temperature. In some embodiments, theintroduced warpage is optimized for zero warpage at solder reflowtemperatures (e.g., 220° C. to 260° C.). is not In some embodiments, theCPA process may be performed at one particular operation in theassembly. In some embodiments, the CPA process is performed at one ormore operations in the IC package assembly.

For a critical attach operation in a particular IC package assembly,Curve 660 may be used to find the residual warpage that results fromthermal cycling with the workpiece constrained. After constructing plot650, the broken lines indicate that at a concave warpage ofapproximately 100 microns magnitude results in a substantially flat ICpackage at 25° C.

FIG. 7 illustrates a method for an exemplary constrained cure IC packageassembly process embodied in flow chart 700, according to embodiments ofthe disclosure.

In FIG. 7, an exemplary constrained IC package assembly (CPA) process isillustrated in flow chart 700, which represents a process flow for a diebackside stiffener attach process. At operation 701, a partiallyassembled IC package is received for stiffener attach. In someembodiments, a die (e.g., 603 in FIG. 6A) is attached to the IC packagesubstrate (e.g. 602 in FIG. 6A).

At operation 702, the partially complete IC package may be prepared forplacement of a stiffener on the die backside. In some embodiments, anadhesive is first applied to the die, then the stiffener is placed onthe adhesive.

At operation 703, the partial IC package assembly is placed in the CPAbonding tool (e.g., 100 in FIG. 6A). In some embodiments, the partial ICpackage assembly workpiece (e.g., 601 in FIG. 6A), is placed on thelower TCB head (e.g., 102 in FIG. 6A). In some embodiments, theworkpiece is placed on a pedestal of a three-point contact constrainedbonding tool (e.g., 200 in FIG. 2). In some embodiments, the workpieceis placed on round spacers (e.g., 303 and 305 of FIG. 3) of athree-point contact constrained bonding tool (e.g. 300 in FIG. 3)constrained between curved TCB heads.

At operation 704, the workpiece is constrained in the CPA bonding tool.In some embodiments, the upper TCB head (e.g., 101 in FIG. 6A) islowered toward the lower TCB head (e.g. 102 in FIG. 6A), pressing itscurved work surface on the workpiece at the center of curvature of theupper TCB head. Enough force is applied to bow the workpiece against thecurved work surface of the lower TCB head, introducing a concave warpagein the workpiece. In some embodiments, the TCB head (e.g. 201 in FIG. 2)is lowered toward the pedestal stand (e.g., 202) in the three-pointcontact constrained bonding tool (e.g., 200 in FIG. 2). Flat spacer onthe TCB head presses the workpiece downward, causing it to bow downward,introducing a concave warpage. In some embodiments, upper TCB head (e.g.301 in FIG. 3) is lowered toward lower TCB head (e.g., 302 in FIG. 3).The center round spacer (e.g., 304 in FIG. 3) presses on the workpiecefrom above, bowing it downward. The action introduces a concave warpageinto the workpiece.

At operation 705, a thermal cycle regime is initiated, heating theworkpiece to a cure temperature for the adhesive. In some embodiments,the temperature is ramped to a maximum value and held for a prescribedperiod of time. In other embodiments, the more than one temperatureplateaus are prescribed for the particular adhesive. Due to thethermocompression bonding, the IC package assembly is permanently bowedout-of-plane into a concave (e.g., downward) or convex (e.g., upward)warped profile in at least one x-y dimension. This operation is carriedout at an elevated temperature, in accordance with some embodiments.According to some embodiments, the operation is conducted at or abovethe cure temperature of the adhesive for a prescribed period allowingsolidification of the adhesive.

At operation 706, the temperature is ramped down to room temperature. Insome embodiments, the adhesive solidifies and holds the constrainedgeometry of the workpiece. At room temperature, a residual warpage inthe IC package may be apparent. In some embodiments, the introducedwarpage during the CPA operation (704) is optimized for solder reflow at260° C. in downstream surface mount of the completed IC package to acircuit board, where the IC package is flat at solder reflowtemperatures for maximizing solder bonding to the circuit board. Thus, aresidual room temperature warpage of the IC package is apparent, and istolerated in some applications because it is more critical that the ICpackage remain flat during surface mount soldering.

At operation 707, the workpiece is removed from the CPA tool. In someembodiments, the workpiece is removed by reversal of operations 703 and704. While process flow 700 is optimized for a constrained die backsidestiffener attach process, it may substantially apply to other IC packagecomponent attach operations. Thus, components such as substratestiffeners, integral heat spreaders (IHS), IHS lidded packages,interposers, both picture frame and blind types, over molded packages,may be substituted for the die backside stiffener.

FIG. 8 illustrates a constrained cure assembled IC package as part of asystem-on-chip (SoC) IC package in an implementation of computingdevice, according to some embodiments of the disclosure.

FIG. 8 illustrates a block diagram of an embodiment of a mobile devicein which flat surface interface connectors could be used. In someembodiments, computing device 800 represents a mobile computing device,such as a computing tablet, a mobile phone or smart-phone, awireless-enabled e-reader, or other wireless mobile device. It will beunderstood that certain components are shown generally, and not allcomponents of such a device are shown in computing device 800.

In some embodiments, computing device 800 includes a first processor810. The various embodiments of the present disclosure may also comprisea network interface within 870 such as a wireless interface so that asystem embodiment may be incorporated into a wireless device, forexample, cell phone or personal digital assistant.

In one embodiment, processor 810 can include one or more physicaldevices, such as microprocessors, application processors,microcontrollers, programmable logic devices, or other processing means.The processing operations performed by processor 810 include theexecution of an operating platform or operating system on whichapplications and/or device functions are executed. The processingoperations include operations related to I/O (input/output) with a humanuser or with other devices, operations related to power management,and/or operations related to connecting the computing device 800 toanother device. The processing operations may also include operationsrelated to audio I/O and/or display I/O.

In one embodiment, computing device 800 includes audio subsystem 820,which represents hardware (e.g., audio hardware and audio circuits) andsoftware (e.g., drivers, codecs) components associated with providingaudio functions to the computing device. Audio functions can includespeaker and/or headphone output, as well as microphone input. Devicesfor such functions can be integrated into computing device 800, orconnected to the computing device 800. In one embodiment, a userinteracts with the computing device 800 by providing audio commands thatare received and processed by processor 810.

Display subsystem 830 represents hardware (e.g., display devices) andsoftware (e.g., drivers) components that provide a visual and/or tactiledisplay for a user to interact with the computing device 800. Displaysubsystem 830 includes display interface 832 which includes theparticular screen or hardware device used to provide a display to auser. In one embodiment, display interface 832 includes logic separatefrom processor 810 to perform at least some processing related to thedisplay. In one embodiment, display subsystem 830 includes a touchscreen (or touch pad) device that provides both output and input to auser.

I/O controller 840 represents hardware devices and software componentsrelated to interaction with a user. I/O controller 840 is operable tomanage hardware that is part of audio subsystem 820 and/or displaysubsystem 830. Additionally, I/O controller 840 illustrates a connectionpoint for additional devices that connect to computing device 800through which a user might interact with the system. For example,devices that can be attached to the computing device 800 might includemicrophone devices, speaker or stereo systems, video systems or otherdisplay devices, keyboard or keypad devices, or other I/O devices foruse with specific applications such as card readers or other devices.

As mentioned above, I/O controller 840 can interact with audio subsystem820 and/or display subsystem 830. For example, input through amicrophone or other audio device can provide input or commands for oneor more applications or functions of the computing device 800.Additionally, audio output can be provided instead of, or in addition todisplay output. In another example, if display subsystem 830 includes atouch screen, the display device also acts as an input device, which canbe at least partially managed by I/O controller 840. There can also beadditional buttons or switches on the computing device 500 to provideI/O functions managed by I/O controller 840.

In one embodiment, I/O controller 840 manages devices such asaccelerometers, cameras, light sensors or other environmental sensors,or other hardware that can be included in the computing device 800. Theinput can be part of direct user interaction, as well as providingenvironmental input to the system to influence its operations (such asfiltering for noise, adjusting displays for brightness detection,applying a flash for a camera, or other features).

In one embodiment, computing device 800 includes power management 850that manages battery power usage, charging of the battery, and featuresrelated to power saving operation. Memory subsystem 860 includes memorydevices for storing information in computing device 800. Memory caninclude nonvolatile (state does not change if power to the memory deviceis interrupted) and/or volatile (state is indeterminate if power to thememory device is interrupted) memory devices. Memory subsystem 860 canstore application data, user data, music, photos, documents, or otherdata, as well as system data (whether long-term or temporary) related tothe execution of the applications and functions of the computing device800.

Elements of embodiments are also provided as a machine-readable medium(e.g., memory 860) for storing the computer-executable instructions. Themachine-readable medium (e.g., memory 860) may include, but is notlimited to, flash memory, optical disks, CD-ROMs, DVD ROMs, RAMs,EPROMs, EEPROMs, magnetic or optical cards, phase change memory (PCM),or other types of machine-readable media suitable for storing electronicor computer-executable instructions. For example, embodiments of thedisclosure may be downloaded as a computer program (e.g., BIOS) whichmay be transferred from a remote computer (e.g., a server) to arequesting computer (e.g., a client) by way of data signals via acommunication link (e.g., a modem or network connection).

Connectivity via network interface 870 includes hardware devices (e.g.,wireless and/or wired connectors and communication hardware) andsoftware components (e.g., drivers, protocol stacks) to enable thecomputing device 800 to communicate with external devices. The computingdevice 800 could be separate devices, such as other computing devices,wireless access points or base stations, as well as peripherals such asheadsets, printers, or other devices.

Network interface 870 can include multiple different types ofconnectivity. To generalize, the computing device 800 is illustratedwith cellular connectivity 872 and wireless connectivity 874. Cellularconnectivity 872 refers generally to cellular network connectivityprovided by wireless carriers, such as provided via GSM (global systemfor mobile communications) or variations or derivatives, CDMA (codedivision multiple access) or variations or derivatives, TDM (timedivision multiplexing) or variations or derivatives, or other cellularservice standards. Wireless connectivity (or wireless interface) 874refers to wireless connectivity that is not cellular, and can includepersonal area networks (such as Bluetooth, Near Field, etc.), local areanetworks (such as Wi-Fi), and/or wide area networks (such as WiMax), orother wireless communication.

Peripheral connections 880 include hardware interfaces and connectors,as well as software components (e.g., drivers, protocol stacks) to makeperipheral connections. It will be understood that the computing device800 could both be a peripheral device (“to” 882) to other computingdevices, as well as have peripheral devices (“from” 884) connected toit. The computing device 800 commonly has a “docking” connector toconnect to other computing devices for purposes such as managing (e.g.,downloading and/or uploading, changing, synchronizing) content oncomputing device 800. Additionally, a docking connector can allowcomputing device 800 to connect to certain peripherals that allow thecomputing device 800 to control content output, for example, toaudiovisual or other systems.

In addition to a proprietary docking connector or other proprietaryconnection hardware, the computing device 800 can make peripheralconnections 880 via common or standards-based connectors. Common typescan include a Universal Serial Bus (USB) connector (which can includeany of a number of different hardware interfaces), DisplayPort includingMiniDisplayPort (MDP), High Definition Multimedia Interface (HDMI),Firewire, or other types.

Reference in the specification to “an embodiment,” “one embodiment,”“some embodiments,” or “other embodiments” means that a particularfeature, structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments. The various appearances of “an embodiment,”“one embodiment,” or “some embodiments” are not necessarily allreferring to the same embodiments. If the specification states acomponent, feature, structure, or characteristic “may,” “might,” or“could” be included, that particular component, feature, structure, orcharacteristic is not required to be included. If the specification orclaim refers to “a” or “an” element, that does not mean there is onlyone of the elements. If the specification or claims refer to “anadditional” element, that does not preclude there being more than one ofthe additional element.

Furthermore, the particular features, structures, functions, orcharacteristics may be combined in any suitable manner in one or moreembodiments. For example, a first embodiment may be combined with asecond embodiment anywhere the particular features, structures,functions, or characteristics associated with the two embodiments arenot mutually exclusive.

While the disclosure has been described in conjunction with specificembodiments thereof, many alternatives, modifications and variations ofsuch embodiments will be apparent to those of ordinary skill in the artin light of the foregoing description. The embodiments of the disclosureare intended to embrace all such alternatives, modifications, andvariations as to fall within the broad scope of the appended claims.

In addition, well known power/ground connections to integrated circuit(IC) chips and other components may or may not be shown within thepresented figures, for simplicity of illustration and discussion, and soas not to obscure the disclosure. Further, arrangements may be shown inblock diagram form in order to avoid obscuring the disclosure, and alsoin view of the fact that specifics with respect to implementation ofsuch block diagram arrangements are highly dependent upon the platformwithin which the present disclosure is to be implemented (i.e., suchspecifics should be well within purview of one skilled in the art).Where specific details (e.g., circuits) are set forth in order todescribe example embodiments of the disclosure, it should be apparent toone skilled in the art that the disclosure can be practiced without, orwith variation of, these specific details. The description is thus to beregarded as illustrative instead of limiting.

The following examples pertain to further embodiments. Specifics in theexamples may be used anywhere in one or more embodiments. All optionalfeatures of the apparatus described herein may also be implemented withrespect to a method or process.

Example 1 is an apparatus, comprising a first platform comprising afirst working surface having a first non-planar portion, and a secondplatform comprising a second working surface having a second non-planarportion, wherein the second working surface is opposite the firstworking surface, a distance between the first working surface and thesecond working surface is adjustable, the first non-planar portioncomprises a protruding portion, and the second non-planar portioncomprises a recessed portion opposite the protruding portion.

Example 2 includes all of the features of example 1, wherein the firstnon-planar portion comprises a first curved portion extending from thefirst platform.

Example 3 includes all of the features of example 2, wherein the secondnon-planar portion comprises a second curved portion recessed into thesecond platform, wherein the second curved portion is opposite the firstcurved portion, and wherein the curvature of the second curved portionis substantially the same as the curvature of the first curved portion.

Example 4 includes all of the features of example 1, wherein the secondnon-planar portion comprises three protrusions comprising a middleprotrusion equidistant between two peripheral protrusions, and wherein az-height of the two peripheral protrusions is larger than z-height ofthe middle protrusion.

Example 5 includes all of the features of example 4, wherein the firstnon-planar portion comprises one protrusion opposite the middleprotrusion of the second non-planar portion.

Example 6 includes all of the features of example 1, wherein the secondnon-planar portion comprises two protrusions separated by a recessedportion of the second non-planar portion.

Example 7 includes all of the features of example 6, wherein the firstnon-planar portion comprises a protrusion opposite the recessed portionof the second non-planar portion.

Example 8 includes all of the features of example 1, wherein the firstplatform is a pedestal that comprises a first cavity.

Example 9 includes all the features of example 8, wherein the firstplatform comprises a protrusion extending from the first non-planarportion opposite the first cavity of the pedestal.

Example 10 includes all of the features of example 8, wherein thepedestal comprises ports extending from the exterior to the firstcavity.

Example 11 includes all of the features of example 10, wherein the portsare vacuum ports.

Example 12 includes all of the features of example 8, wherein the secondplatform comprises a second cavity opposite the first cavity of thepedestal.

Example 13 includes all of the features of example 12, wherein thesecond cavity is a pressure chamber.

Example 14 includes all of the features of example 1, wherein the firstplatform is a thermocompression bond head.

Example 15 includes all of the features of example 1, wherein the secondplatform is a thermocompression bonding head.

Example 16 is a method comprising receiving a partially assembled ICpackage comprising an IC package substrate, placing an adhesive over theIC package substrate, attaching a IC package component on the adhesive,warping the partially assembled IC package out-of-plane, and curing theadhesive.

Example 17 includes all of the features of example 16, wherein warpingthe partially assembled IC package out-of-plane comprises introducing apredetermined curvature in the partially assembled IC package.

Example 18 includes all of the features of example 17, whereinintroducing a predetermined curvature in the partially assembled ICpackage comprises constraining the partially assembled IC packagebetween non-planar working surfaces.

Example 19 includes all of the features of example 17, wherein warpingthe partially assembled IC package out-of-plane comprises constrainingthe partially assembled IC package between opposing thermocompressionbonding heads having non-planar working surfaces.

Example 18 includes all of the features of example 16, wherein warpingthe partially assembled IC package out-of-plane comprises introducing apredetermined curvature in the partially assembled IC package.

Example 19 includes all of the features of example 17, whereinintroducing a predetermined curvature in the partially assembled ICpackage comprises constraining the partially assembled IC packagebetween opposing thermocompression bonding heads having non-planarworking surfaces.

Example 20 includes all of the features of example 19, wherein thenon-planar working surfaces of the opposing thermocompression bondingheads comprise opposing curved portions having substantially a samecurvature.

Example 21 includes all of the features of examples 19 or 20,constraining the partially assembled IC package between the non-planarwork surfaces of the opposing thermocompression bonding heads comprisesuspending the IC package substrate between two pedestals of a lowerthermocompression bonding head and pressing on the partially assembledIC package by a protrusion extending from the working surface of anupper thermocompression bonding head.

Example 22 includes all of the features of examples 17 or 18, whereinintroducing a predetermined curvature in the partially assembled ICpackage comprises suspending the partially assembled IC package over acavity and applying a vacuum in the cavity.

Example 23 includes all of the features of examples 17 or 18, whereinintroducing a predetermined curvature in the partially assembled ICpackage comprises suspending the partially assembled IC package under achamber and applying pressure over the partially assembled IC package.

Example 24 includes all of the features of any one of examples 17through 23, wherein introducing a predetermined curvature in thepartially assembled IC package comprises determining an optimalmagnitude of warpage to introduce into the partially assembled ICpackage by constraining the partially assembled IC package betweennon-planar working surfaces. by correlating a magnitude of warpage at atemperature of a IC package comprising the partially assembled ICpackage with a magnitude of warpage introduced into the partiallyassembled IC package.

Example 25 includes all of the features of example 16, wherein curingthe adhesive comprises solidifying the adhesive at an elevated curingtemperature to induce a warpage in the partially assembled IC package ator above a curing temperature of the adhesive.

Example 26 is a system comprising a memory, a processor coupled to thememory, wherein the memory and processor are integrated into a ICpackage comprising a substrate having a first surface and an opposingsecond surface, one or more dies attached to the first surface of thesubstrate, wherein the first surface of the substrate and at least oneof the one or more dies are warped at a specified temperature, and awireless interface communicatively coupled to the IC package, thewireless interface to allow the processor to communicate with anotherdevice.

Example 27 includes all of the features of example 26, wherein the ICpackage comprises a thin stiffener.

Example 28 includes all of the features of examples 26 or 27, whereinthe IC package has a zero warpage at a specified temperature.

Example 29 includes all of the features of example 26, wherein thespecified temperature is one of approximately 20° C. or approximately260° C.

Example 30 includes all of the features of example 26, wherein thespecified temperature ranges between 20° C. and 260° C.

An abstract is provided that will allow the reader to ascertain thenature and gist of the technical disclosure. The abstract is submittedwith the understanding that it will not be used to limit the scope ormeaning of the claims. The following claims are hereby incorporated intothe detailed description, with each claim standing on its own as aseparate embodiment.

We claim:
 1. An apparatus, comprising: a first platform comprising afirst working surface having a first non-planar portion, wherein thefirst non-planar portion comprises a first curved portion extending fromthe first platform; and a second platform comprising a second workingsurface having a second non-planar portion, wherein the secondnon-planar portion comprises a second curved portion recessed into thesecond platform, wherein the second curved portion is opposite the firstcurved portion, and wherein the curvature of the second curved portionis substantially the same as the curvature of the first curved portion,and wherein: the second working surface is opposite the first workingsurface, a distance between the first working surface and the secondworking surface is adjustable, the first non-planar portion comprises aprotruding portion; and the second non-planar portion comprises arecessed portion opposite the protruding portion.
 2. The apparatus ofclaim 1, wherein the first platform comprises a first thermocompressionbonding head.
 3. The apparatus of claim 2, wherein the second platformcomprises a second thermocompression bonding head opposing the firstthermocompression bonding head.
 4. The apparatus of claim 3, wherein thesecond thermocompression bonding head has a second curved workingsurface, and wherein the second curved working surface has a curvaturethat is complimentary to a curvature of the first curved workingsurface.
 5. The apparatus of claim 2, wherein the firstthermocompression bonding head has a first curved working surface.
 6. Anapparatus, comprising: a first platform comprising a first workingsurface having a first non-planar portion; and a second platformcomprising a second working surface having a second non-planar portion,wherein: the second working surface is opposite the first workingsurface, a distance between the first working surface and the secondworking surface is adjustable, the first non-planar portion comprises aprotruding portion, and the second non-planar portion comprises arecessed portion opposite the protruding portion, wherein the secondnon-planar portion comprises three protrusions comprising a middleprotrusion equidistant between two peripheral protrusions, and wherein az-height of the two peripheral protrusions is larger than a z-height ofthe middle protrusion.
 7. The apparatus of claim 6, wherein the firstnon-planar portion comprises one protrusion opposite the middleprotrusion of the second non-planar portion.
 8. The apparatus of claim6, wherein the second non-planar portion comprises two protrusionsseparated by a recessed portion of the second non-planar portion.
 9. Theapparatus of claim 8, wherein the first non-planar portion comprises aprotrusion opposite the recessed portion of the second non-planarportion.
 10. An apparatus, comprising: a first platform comprising afirst working surface having a first non-planar portion; and a secondplatform comprising a second working surface having a second non-planarportion, wherein: the second working surface is opposite the firstworking surface, a distance between the first working surface and thesecond working surface is adjustable, the first non-planar portioncomprises a protruding portion, and the second non-planar portioncomprises a recessed portion opposite the protruding portion, whereinthe first platform comprises a first cavity, and wherein the firstplatform comprises ports extending from an exterior wall of the firstplatform to the first cavity.
 11. The apparatus of claim 10, wherein thesecond platform comprises a protrusion extending from the secondnon-planar portion opposite the first cavity of the first platform. 12.The apparatus of claim 11, wherein the protrusion is a stylus.
 13. Theapparatus of claim 10, wherein the second platform comprises a secondcavity opposite the first cavity of the first platform.
 14. Theapparatus of claim 13, wherein the second cavity is a pressure chamber.15. The apparatus of claim 10, wherein the ports are vacuum ports.